The Link header was originally designed to let browsers know that they should preload an asset. If you still need this behavior for legacy reasons, you can append the nopush directive to the header, like so:

Generates a list of local static resources used in your web app by outputting a json file. This file can be read by your web server to more easily construct the appropriate Link: <URL>; rel=preload; as=<TYPE> headers(s) for http2 push/preload.

LoadCSS is designed for loading CSS that is not critical to the initial rendering of the page, and desirable to load in an asynchronous manner. (For the critical CSS rules, we recommend either inlining that CSS in a style element, or referencing it externally and server-pushing it using http/2. Read more here)

The standard markup pattern for loading files asynchronously is: <link rel="preload"> (W3C Spec). We recommend using this markup pattern to reference your non-critical CSS files. loadCSS and its rel=preload polyfill are designed to enable this markup to work in browsers that don't yet support this feature.